ViewGroup的Touch事件分发(源码分析)

Android中Touch事件的分发又分为View和ViewGroup的事件分发，View的touch事件分发相对比较简单，可参考

View的Touch事件分发(一.初步了解) View的Touch事件分发(一.初步了解)_yinianzhijian99的专栏-CSDN博客

View的Touch事件分发(二.源码分析) View的Touch事件分发(二.源码分析)_yinianzhijian99的专栏-CSDN博客

现在开始分析ViewGroup的Touch事件分发

现象：给一个控件设置OnTouchListener和OnClickListener，点击控件，会有以下结果：

1.正常情况下

手指按下

DOWN ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent ->

View.dispatchTouchEvent -> View.onTouch -> View.onTouchEvent

手指移动

MOVE ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent ->

View.dispatchTouchEvent -> View.onTouch -> View.onTouchEvent

手指抬起

UP ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent ->

View.onTouch -> View.onTouchEvent -> View.onclick

2.onClick没有,理解为没有消费事件

ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent -

> View.dispatchTouchEvent -> View.onTouch -> View onTouchEvent -

> ViewGroup.onTouchEvent

3.在View的onTouchEvent()方法里面返回true的情况下

手指按下

DOWN ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent ->

View.dispatchTouchEvent -> View.onTouch -> View.onTouchEvent

手指移动

MOVE ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent ->

View.dispatchTouchEvent -> View.onTouch -> View.onTouchEvent

手指抬起

UP ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent ->

View.onTouch -> View.onTouchEvent

4.在ViewGroup的onInterceptTouchEvent()方法里面返回true的情况下

ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent -> ViewGroup.onTouchEvent

源码分析：

ViewGroup的Touch事件是从Activity的dispatchTouchEvent()方法开始的

Activity的dispatchTouchEvent()方法如下:

public boolean dispatchTouchEvent(MotionEvent ev) {if (ev.getAction() == MotionEvent.ACTION_DOWN) {onUserInteraction();}if (getWindow().superDispatchTouchEvent(ev)) {return true;}return onTouchEvent(ev);
}

getWindow()是mWindow，mWindow = new PhoneWindow(this);

进入PhoneWindow的superDispatchTouchEvent()方法：

@Override
public boolean superDispatchTouchEvent(MotionEvent event) {return mDecor.superDispatchTouchEvent(event);
}

DecorView继承了FrameLayout，最终会调用ViewGroup的dispatchTouchEvent()方法：

@Override
public boolean dispatchTouchEvent(MotionEvent ev) {if (mInputEventConsistencyVerifier != null) {mInputEventConsistencyVerifier.onTouchEvent(ev, 1);}// If the event targets the accessibility focused view and this is it, start// normal event dispatch. Maybe a descendant is what will handle the click.if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) {ev.setTargetAccessibilityFocus(false);}//是否被消费boolean handled = false;if (onFilterTouchEventForSecurity(ev)) {final int action = ev.getAction();final int actionMasked = action & MotionEvent.ACTION_MASK;// Handle an initial down.if (actionMasked == MotionEvent.ACTION_DOWN) {// Throw away all previous state when starting a new touch gesture.// The framework may have dropped the up or cancel event for the previous gesture// due to an app switch, ANR, or some other state change.//对一些变量重置，清除TouchTargets，mFirstTouchTarget = nullcancelAndClearTouchTargets(ev);resetTouchState();}// Check for interception.//检查是否需要拦截touch事件//mFirstTouchTarget是ViewGroup的一个内部类封装了被触摸的view//mFirstTouchTarget不为空表示有子View消费touch事件//mFirstTouchTarget为空表示ViewGroup拦截了touch事件或者子view没有消费touch事件final boolean intercepted;if (actionMasked == MotionEvent.ACTION_DOWN|| mFirstTouchTarget != null) {final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;if (!disallowIntercept) {//根据onInterceptTouchEvent()方法的返回值来决定是否拦截touch事件intercepted = onInterceptTouchEvent(ev);ev.setAction(action); // restore action in case it was changed} else {intercepted = false;}} else {// There are no touch targets and this action is not an initial down// so this view group continues to intercept touches.//如果不是ACTION_DOWN并且没有子view消费掉touch事件,拦截touch事件//如果ACTION_DOWN没有被子view消费,//那么接下来的ACTION_MOVE,ACTINO_UP就都不会走onInterceptTouchEvent()方法//将intercepted设置为true直接进行拦截交给自身进行touch事件的处理(dispatchTouchEvent() -> onTouch() -> onTouchEvent())intercepted = true;}// If intercepted, start normal event dispatch. Also if there is already// a view that is handling the gesture, do normal event dispatch.if (intercepted || mFirstTouchTarget != null) {ev.setTargetAccessibilityFocus(false);}// Check for cancelation.//检查cancel状态final boolean canceled = resetCancelNextUpFlag(this)|| actionMasked == MotionEvent.ACTION_CANCEL;// Update list of touch targets for pointer down, if needed.final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;TouchTarget newTouchTarget = null;boolean alreadyDispatchedToNewTouchTarget = false;if (!canceled && !intercepted) {// If the event is targeting accessiiblity focus we give it to the// view that has accessibility focus and if it does not handle it// we clear the flag and dispatch the event to all children as usual.// We are looking up the accessibility focused host to avoid keeping// state since these events are very rare.View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus()? findChildWithAccessibilityFocus() : null;if (actionMasked == MotionEvent.ACTION_DOWN|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {final int actionIndex = ev.getActionIndex(); // always 0 for downfinal int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex): TouchTarget.ALL_POINTER_IDS;// Clean up earlier touch targets for this pointer id in case they// have become out of sync.removePointersFromTouchTargets(idBitsToAssign);final int childrenCount = mChildrenCount;if (newTouchTarget == null && childrenCount != 0) {计算touch点的坐标根据touch点坐标判断当前触摸到的是哪个子viewfinal float x = ev.getX(actionIndex);final float y = ev.getY(actionIndex);// Find a child that can receive the event.// Scan children from front to back.final ArrayList<View> preorderedList = buildOrderedChildList();final boolean customOrder = preorderedList == null&& isChildrenDrawingOrderEnabled();final View[] children = mChildren;注意是从后往前进行遍历 最后面的child是最上层的viewfor (int i = childrenCount - 1; i >= 0; i--) {final int childIndex = customOrder? getChildDrawingOrder(childrenCount, i) : i;final View child = (preorderedList == null)? children[childIndex] : preorderedList.get(childIndex);// If there is a view that has accessibility focus we want it// to get the event first and if not handled we will perform a// normal dispatch. We may do a double iteration but this is// safer given the timeframe.if (childWithAccessibilityFocus != null) {if (childWithAccessibilityFocus != child) {continue;}childWithAccessibilityFocus = null;i = childrenCount - 1;}if (!canViewReceivePointerEvents(child)|| !isTransformedTouchPointInView(x, y, child, null)) {ev.setTargetAccessibilityFocus(false);continue;}newTouchTarget = getTouchTarget(child);if (newTouchTarget != null) {// Child is already receiving touch within its bounds.// Give it the new pointer in addition to the ones it is handling.newTouchTarget.pointerIdBits |= idBitsToAssign;//已经找到了接收touch事件的子view,不用再继续遍历break;}resetCancelNextUpFlag(child);//dispatchTransformedTouchEvent()中调用了child.dispatchTouchEvent()方法//根据child.dispatchTouchEvent()方法的返回值判断子view是否消费了touch事件if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {// Child wants to receive touch within its bounds.mLastTouchDownTime = ev.getDownTime();if (preorderedList != null) {// childIndex points into presorted list, find original indexfor (int j = 0; j < childrenCount; j++) {if (children[childIndex] == mChildren[j]) {mLastTouchDownIndex = j;break;}}} else {mLastTouchDownIndex = childIndex;}mLastTouchDownX = ev.getX();mLastTouchDownY = ev.getY();newTouchTarget = addTouchTarget(child, idBitsToAssign);//为true表示此时已经将touch事件分发给了子view,即子view消费了touch事件alreadyDispatchedToNewTouchTarget = true;break;}// The accessibility focus didn't handle the event, so clear// the flag and do a normal dispatch to all children.ev.setTargetAccessibilityFocus(false);}if (preorderedList != null) preorderedList.clear();}if (newTouchTarget == null && mFirstTouchTarget != null) {// Did not find a child to receive the event.// Assign the pointer to the least recently added target.newTouchTarget = mFirstTouchTarget;while (newTouchTarget.next != null) {newTouchTarget = newTouchTarget.next;}newTouchTarget.pointerIdBits |= idBitsToAssign;}}}// Dispatch to touch targets.if (mFirstTouchTarget == null) {// No touch targets so treat this as an ordinary view.handled = dispatchTransformedTouchEvent(ev, canceled, null,TouchTarget.ALL_POINTER_IDS);} else {// Dispatch to touch targets, excluding the new touch target if we already// dispatched to it.  Cancel touch targets if necessary.TouchTarget predecessor = null;TouchTarget target = mFirstTouchTarget;while (target != null) {final TouchTarget next = target.next;if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {handled = true;} else {final boolean cancelChild = resetCancelNextUpFlag(target.child)|| intercepted;if (dispatchTransformedTouchEvent(ev, cancelChild,target.child, target.pointerIdBits)) {handled = true;}if (cancelChild) {if (predecessor == null) {mFirstTouchTarget = next;} else {predecessor.next = next;}target.recycle();target = next;continue;}}predecessor = target;target = next;}}// Update list of touch targets for pointer up or cancel, if needed.//在ACTION_UP手指抬起或者ACTION_CANCEL取消touch事件分发,恢复重置一些状态if (canceled|| actionMasked == MotionEvent.ACTION_UP|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {resetTouchState();} else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {final int actionIndex = ev.getActionIndex();final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);removePointersFromTouchTargets(idBitsToRemove);}}if (!handled && mInputEventConsistencyVerifier != null) {mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);}return handled;
}

整个touch事件的传递过程为: Activity.dispatchTouchEvent() -> PhoneWindow.superDispatchTouchEvent() -> DecorView.superDispatchTouchEvent() -> ViewGroup.dispatchTouchEvent() -> View.dispatchTouchEvent()

而消费过程则相反: View.onTouchEvent() -> ViewGroup.onTouchEvent() -> DecorView.onTouchEvent() -> Activity.onTouchEvent()

如果子View没有一个地方返回true，touch事件只会进来一次，只会响应DOWN事件，代表不需要消费该事件，如果你想响应MOVE或UP必须找个地方ture。

对于ViewGroup来讲，如果你想拦截子View的Touch事件，可以覆写onInterceptTouchEvent，返回true即可。

如果onInterceptTouchEvent返回的是true,会执行该ViewGroup的onTouchEvent方法 , 如果子View没有消费touch事件，也会调用该ViewGroup的onTouchEvent 方法。

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